The present invention relates to a pneumatic, two-layer detector for use in NDIR (Non-dispersive Infrared) gas analyzers having two, coaxially arranged, gas-filled chambers with radiation permeable frontal areas, a line which couples the chambers, and a pressure or flow-rate sensor of a pneumo-electrical transducer arranged in the line.
These types of detectors are employed in gas analyzers, in which modulated infrared (IR) radiation strikes the detector through a cuvette filled with the gas being analyzed. As a rule, the gas being analyzed is a gas mixture having one or more components to be evaluated. The components to be evaluated or a gas having the same kind of absorptive capacity for IR-radiation constitute the gas filling in the detector chambers (see, e.g., German Patent 1 017 385).
Distortions in the measuring-signal occur because of so-called "cross sensitivity". That is, there are instances when the absorption bands of other components contained in the gas being analyzed overlap with those of the component to be measured. The known two-layer detector configuration, in which the two chambers are pneumatically connected back to back, improves the selectivity ratio. In this manner, the sensitivity due to the absorption bands of all disturbing components may be reduced but can not be totally eliminated. Thus there is a need for a detector for use in a gas analyzer which eliminates cross-sensitivity due to the absorption bands of other components contained in the gas being analyzed.